PLoS One. 2014 Jun 18;9(6):e97452.

P2X7 Receptor in the Kidneys of Diabetic Rats Submitted to Aerobic Training or to N-acetylcysteine Supplementation

Adelson M Rodrigues, PhD *; Cassia T Bergamaschi, PhD &; Maria Jose S Fernandes, PhD @; Edgar J Paredes-Gamero, PhD %; Marcus V Buri, MSc %; Alice T Ferreira, MD PhD £; Sergio R R Araujo, PhD$; Giovana R Punaro, MSc*; Fabiane R Maciel*; Guilherme B Nogueira*; Elisa M S Higa, MD PhD*, #.

* Department of Medicine, Nephrology Division, UNIFESP, Sao Paulo, Brazil.
& Department of Physiology, Cardiovascular Division, UNIFESP, Sao Paulo, Brazil.
@Department of Neurology / Neurosurgery, UNIFESP, Sao Paulo, Brazil.
% Department of Biochemistry, UNIFESP, Sao Paulo, Brazil.
£ Department of Biophysics, Molecular Biology Division, UNIFESP, Sao Paulo, Brazil.
$ Department of Pathology, Investigative Pathology Division, UNIFESP, Sao Paulo, Brazil.
# Department of Medicine, Emergency Division, UNIFESP, Sao Paulo, Brazil.

 

Abstract

Previous studies in our laboratory showed that N-acetylcysteine supplementation or aerobic training reduced oxidative stress and the progression of diabetic nephropathy in rats. The P2X7 receptor is up-regulated in pathological conditions, such as diabetes mellitus. This up-regulation is related to oxidative stress and induces tissue apoptosis or necrosis. The aim of the present study is to assess the role of P2X7 receptor in the kidneys of diabetic rats submitted to aerobic training or N-acetylcysteine supplementation. Diabetes was induced in male Wistar rats by streptozotocin (60 mg/kg, i.v.) and the training was done on a treadmill; N-acetylcysteine was given in the drinking water (600 mg/L). By confocal microscopy, as compared to control, the kidneys of diabetic rats showed increased P2X7 receptor expression and a higher activation in response to 2′(3′)-O-(4-benzoylbenzoyl) adenosine5′-triphosphate (specific agonist) and adenosine triphosphate (nonspecific agonist) (all p<0.05). All these alterations were reduced in diabetic rats treated with N-acetylcysteine, exercise or both. We also observed measured proteinuria and albuminuria (early marker of diabetic nephropathy) in DM groups. Lipoperoxidation was strongly correlated with P2X7 receptor expression, which was also correlated to NO•, thus associating this receptor to oxidative stress and kidney lesion. We suggest that P2X7 receptor inhibition associated with the maintenance of redox homeostasis could be useful as coadjuvant treatment to delay the progression of diabetic nephropathy.

PMID: 24940871

 

SUPLEMMENTARY

Diabetes mellitus (DM) is an emerging global health problem; thirty percent of diabetic patients develop nephropathy, which is one of the major factors contributing to morbidity and mortality in these patients (1).

Many factors appear to contribute to the pathophysiology of DM, as for example, Thaning and colleagues (2) demonstrated that the vasodilatatory effect of the purinergic (P2) receptors is attenuated in these patients. These P2 receptors are formed mainly by receptors sensitive to extracellular ATP, and comprise two subfamilies, P2Y and P2X. The P2X subgroup consists of seven members (P2X1–7), which act as ligand-gated ion channels, mediating rapid changes in membrane permeability to cations (3).

The P2X7 receptor have two transmembrane domains, a large extracellular loop, and intracellular N and C termini (4). The C termini of the various P2X subunits vary in length, the P2X7 receptor has 240 amino acids which are associated with the functional properties specific to each receptor (5) (figure 1).

 

p2x7Figure 1. Illustration of P2X7 receptor with extracellular loop and domains.

porosityFigure 2. Image adapted from

 

Several roles for the P2X7 receptor have been proposed, but its physiological significance is largely unknown. The permeability increase caused by activation of the P2X7-like receptor results in large ion fluxes and leakage of small metabolites, which on prolonged stimulation may cause cell swelling, vacuolization, and cell death by necrosis or apoptosis (6).

The present study suggests that the use of strategies that modulate P2X7 receptor, such as N-acetilcysteine or aerobic training, especially when both are associated, result in renoprotective action, reducing diabetic nephropathy. Our findings showed that P2X7 receptor expression was strongly correlated with lipoperoxidation, which is corroborated by others studies that have demonstrated that this receptor can induce reactive oxygen and nitrogen species production (7). However, there are no studies that show the opposite, in other words, whether redox homeostasis compromise the P2X7 receptor activation is unclear.

To our knowledge, this study is the first to show the possible modulation of P2X7 receptor by nitric oxide, because we have seen that when oxidative stress is reduced, nitric oxide bioavailability is increased; and in this situation the nitric oxide could perhaps be inhibiting the receptor through its nitrosylation. We believe that these findings need further investigations to identify the intracellular pathways that would modulate P2X7 receptor activity, providing therapeutic targets to the prevention of diabetic complications.

 

REFERENCES

  1. Molitch ME, DeFronzo RA, Franz MJ, Keane WF, Mogensen CE, Parving HH, et al. Nephropathy in diabetes. Diabetes Care. 2004;27 Suppl 1:S79-83.
  2. Thaning P, Bune LT, Hellsten Y, Pilegaard H, Saltin B, Rosenmeier JB. Attenuated purinergic receptor function in patients with type 2 diabetes. Diabetes. 2010;59(1):182-9.
  3. Vonend O, Turner CM, Chan CM, Loesch A, Dell’Anna GC, Srai KS, et al. Glomerular expression of the ATP-sensitive P2X receptor in diabetic and hypertensive rat models. Kidney Int. 2004;66(1):157-66.
  4. North RA. Molecular physiology of P2X receptors. Physiol Rev. 2002;82(4):1013-67.
  5. Kellenberger S, Grutter T. Architectural and Functional Similarities between Trimeric ATP-Gated P2X Receptors and Acid-Sensing Ion Channels. J Mol Biol. 2014.
  6. Ralevic V, Burnstock G. Receptors for purines and pyrimidines. Pharmacol Rev. 1998;50(3):413-92.
  7. Hewinson J, Mackenzie AB. P2X(7) receptor-mediated reactive oxygen and nitrogen species formation: from receptor to generators. Biochem Soc Trans. 2007;35(Pt 5):1168-70.

 

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